The present invention relates in general to noise reducing and sound dampening structures and attachments which can be applied to specific components and at specific locations in order to reduce or muffle the sound level which would otherwise be transmitted. More specifically the present invention relates to reducing the operation and vibration noises caused by the oil pan of a large diesel engine. This reduction in the noise level is achieved by adding a sound dampening enclosure to and around the oil pan.
Noise levels are a concern in most motor vehicles and considerable attention has been given to ways to reduce the noise levels coming from a variety of engine and vehicle locations. While the specific sources of noise may be much the same for a number of vehicles, the actual noise levels often depend on size, materials, and the specific location or mounting provisions for a particular component. For example, the oil pan can be a significant source of noise as it vibrates in response to the operation of the vehicle and vehicle vibrations. With a relatively small engine, such as that typically found in a passenger car, the size of the required oil pan is also relatively small. This smaller size results in a stiffer oil pan design and a higher natural frequency which prevents, for the most part, the oil pan from responding to engine vibration and producing sound in a manner similar to a drum.
When the size of the oil pan is increased, such as that required for a large diesel truck engine, the walls of the pan lose some of their stiffness and the oil pan has a lower natural frequency. When the oil pan then vibrates at its natural frequency, it behaves much like a bass drum and the vibration noise created by the oil pan becomes a concern, since most large diesel engine excitations have relatively low frequencies. This oil pan noise adds to the total noise level of the engine and it is this noise level which engine and vehicle designers are continually addressing in an effort to keep such noise levels at a minimum. It would therefore be an improvement to the reduction of engine/vehicle noise if the noise level caused by the oil pan could be reduced.
While there are several options to reduce the noise levels caused by the oil pan, none of the earlier attempts by others to mechanically attach a noise enclosure to an oil pan are believed to be suitable when the entirety of the oil pan design and vehicle servicing are considered. For example, it would be an improvement to unitize the assembly of a sound deadening enclosure to the oil pan such that when the oil pan is removed for servicing, the enclosure stays attached to the oil pan. Another improvement would be to enable the enclosure to be removed in the event it becomes damaged. A further improvement would be to better impede the transmission of noise from the pan to the enclosure through the attachment system.
While sound insulation panels are known to exist, they often consist of a relatively flat panel which is fixed directly to the noise-generating member, such as directly to a surface of the engine. This type of design is represented by Japanese patent reference No. 58-162729(A) (application No. 57-45899) which was published Sep. 27, 1983 and filed by Nissan Motor Company. This reference provides a non-contact sound insulation plate 17 which is made of a high damping material and pressed securely on the outer surface of the engine with a bracket. When the bracket is compressively mounted directly to the engine, this attachment scheme can also transmit vibrations. If a rigid attachment system is used to attach the outer skin, then the bracket or mounting studs will simply transfer the engine vibration directly to the outer skin and the noise will not be reduced as much as if the outer skin attachment system isolates the outer skin in some way. The relatively rigid outer skin is what blocks the sound. It acts as a very low pass filter. The layer of foam is used to isolate the outer skin from the oil pan.
While some of these issues may be less of a concern if we are only applying a sound insulation panel to an engine surface, the oil pan presents a more significant challenge. In trying to reduce vibration noise generated by a large diesel engine oil pan, vehicle servicing and removal of the oil pan have to be considered. If the enclosure is not securely assembled to the oil pan as a single unit, then the enclosure and its mounting hardware will have to be separately handled and stored during servicing. If the oil pan mounting screws are not accessible due to the manner in which the enclosure is designed, then the sound insulation enclosure will have to be removed in order to provide access to the mounting screws for removal of the oil pan. Whenever the enclosure is separated from the oil pan, such as during this type of servicing, there is a risk that the enclosure will not be reassembled to the oil pan.
There are obviously a number of significant design considerations in trying to design a suitable sound insulation enclosure for a large oil pan. While this task is significant, the present invention does provide a unique combination of components which achieves all of the design objectives and overcomes the various problems which have been mentioned.
In addition to Japanese reference No. 58-162729(A), there are other patents which are concerned with noise reduction and the following listing is believed to be a representative sampling of such other patents:
______________________________________ PATENT NO. PATENTEE ISSUE DATE ______________________________________ 3,693,602 Thien et al. Sep. 26, 1972 4,412,516 Hayashi Nov. 1, 1983 4,619,343 Lengenfelder Oct. 28, 1986 UK 2,066,358 Jul. 8, 1981 UK 669,269 Apr. 2, 1952 ______________________________________
Since the present invention uses a clip design to help secure the enclosure to the oil pan, other patents have been considered for their disclosure of fastening arrangements using clips and spring clamps. The following listing of U.S. patents is believed to be a representative sampling of these earlier fastener designs:
______________________________________ U.S. Pat. No. PATENTEE ISSUE DATE ______________________________________ 324,619 Wells Aug. 18, 1885 4,677,947 Bousquet Jul. 7, 1987 4,709,670 Ampferer Dec. 1, 1987 ______________________________________